Genes that make both a mother and her fetus more susceptible to inflammation as a result of infections raise the risk of premature delivery, a finding that may help explain why some women give birth prematurely even though they have seemingly done everything right during their pregnancies. The genes may be an evolutionary response to infections during pregnancy, in effect causing the baby to be expelled prematurely in an effort to save the mother's life, according to Dr. Roberto Romero of the National Institute of Child Health and Human Development.
Premature births -- before the 37th week of gestation -- are a continuing problem worldwide. An estimated 500,000 babies in the United States and about 13 million worldwide are born prematurely each year, with complications that include delayed neurological and behavioral development, breathing problems, bleeding into the brain and other difficulties. By some estimates, as many as a third of all pregnant women suffer from undetected infections of the uterus during their pregnancy.
Romero and his colleagues studied 190 genes and more than 700 DNA mutations in 229 women who delivered prematurely and in 179 premature babies in Chile, comparing them with 600 women whose gestation went full-term. Romero reported this week at a Chicago meeting of the Society for Maternal-Fetal Medicine that several genetic variations were assocaited with preterm birth, but two stood out. In fetuses, a variation in the interleukin 6 receptor, which is involved in the body's response to inflammation, was most closely associated with prematurity. In the mother, the strongest association was with a gene called tissue inhibitor of metalloproteinase 2, which also plays a role in the inflammatory response.
The findings "add evidence that individual genetic variation in that [inflammatory] response may account for why preterm birth occurs in some pregnancies and not in others," Dr. Alan E. Guttmacher, acting director of the institute, said in a statement.
Romero hopes eventually to develop a genetic test that will allow physicians to identify those women at greatest risk of a preterm delivery.
-- Thomas H. Maugh II
Photo: Infants born prematurely are small and usually face a number of health risks. Credit: Ken Hively / Los Angeles Times